1. Field of the Invention
This invention relates to a surgical electrode and, more particularly, to a temporary cardiac pacing wire having a partially insulated needle to enhance its safety.
2. Description of the Related Art
Devices to stimulate or regulate cardiac function have been known and used for decades. They involve a power source (pacemaker) and a surgical electrode to attach the source to the heart. They are generally of two types.
Implantable pacers are intended for long-term use and, as the name suggests, are entirely implanted in the body. The other type is intended for temporary use. The pacemaker is located outside the body and is connected to the heart by a surgical electrode called a "temporary pacing wire". Although surgical electrodes are used for preparing electrocardiograms and other applications, for the sake of brevity, the description that follows is focused on temporary cardiac pacing wires. In general, such connectors are constructed of a number of fine, stainless steel wires twisted together to form a single, flexible, multifilament electrode wire. The major portion of the wire is insulated with a polyethylene, polytetrafluoroethylene, silicone, nylon, or other non-conducting coating, with a short length of wire at either end left uninsulated. To one uninsulated end of the electrode wire there is attached by swaging or other means a fine curved needle for piercing the heart tissue to place the uninsulated end of the electrode in the myocardium. At the other end of the electrode wire is affixed a straight (e.g., Keith-type) cutting needle for piercing the thoracic wall to lead the electrode to an outer point for connection with the pacemaker. Once that has been accomplished, the needle, or the sharp, pointed end of it, is clipped off and the electrode is ready to be attached to the pacemaker as required to stimulate or regulate the beating of the heart. A single setup involves two electrodes; i.e., two temporary pacing wires.
Temporary pacing wires have been described in a number of patents. U.S. Pat. No. 4,010,756, issued on Mar. 8, 1977 to DuMont et al., discloses a surgical electrode that has a weakened zone in the straight needle that pierces the body when the pacing wire is put in place. The weakened zone permits the pointed end of the needle to be snapped off and the remaining shank to be used as a jack and connected to a pacemaker. A disadvantage of this design is that the shank end can have a burr that could cause minor injuries to a healthcare worker. A more serious concern is that the bare shank could inadvertently be inserted into an inappropriate power source (such as a wall outlet) with very serious consequences. Another danger is that the two electrodes of a setup, protruding from a pacemaker, could be accidentally shorted; for example, by a surgical instrument.
U.S. Pat. No. 4,442,840, issued on Apr. 17, 1984 to Wojciechowicz, discloses a connector that attaches to the shank of the straight needle after it has been clipped or broken off from the sharp end. The connector can then be connected to a mating receptacle on a medical instrument for diagnosis or therapy. (Another type of connector for a temporary pacing wire is disclosed in U.S. Pat. No. 5,795,178, issued on Aug. 18, 1998 to Schilder et al.) Connectors that attach to the free end of a temporary pacing wire (after the sharp end of the straight needle has been removed) provide some advantages, but they require additional effort to attach and involve additional expense.
U.S. Pat. No. 4,630,617, issued on Dec. 23, 1986 to Ritter et al., discloses a surgical electrode whose straight-needle end has a blind hole or flange on the nonpointed end. The hole or flange holds a blunt-pointed pin with controlled pull-out characteristics. Thus, the pin can be pulled out and used as a jack for connecting to a pacemaker or other device. The fact that this device must contain a blunt-pointed pin within a member that necessarily has a larger diameter requires that the straight needle shaft be relatively large. This, in turn, increases the trauma caused when the needle passes through the thoracic wall during placement.
Prior art systems for connecting temporary pacing wires to pacemakers fall into two categories. Simple ("connector-free") systems pose actual and/or potential harm to the cardiac patient. Systems that use connectors require the additional step of attaching the connector, as well as the additional cost of the connector.